Railway signaling system



Sept. 29, 1942. H, s. YOUNG ETAL RAILWAY SIGNALING SYSTEM Filed April30, 1941 2 Sheets-Sheet l @4 su L WR www mi uw HL u A @l w L Wm Il A@ mwDEP@ WIMN INVENTORS Hmpy oungand 120ml BY i .McCann THEIR ATRNY uw unasept. 29, 1942.

H. S. YOUNG ET AL RAILWAY S IGNALING SYSTEM Filed April 30, 1941 2Sheets-Sheet 2 INVENTORS H0121@ Szmg 0111130120 AMC'Ca/zm THEIRATT'oRNEY Patented Sept. 29, 1942 RAILWAY SGNALING SYSTEM Henry S.Young, Wilkinsburg, and Ronald A. Mc-

Cann. Swissvale, Pa., assgnors to The Union Switch & Signal Company,Swissvale, Pa., a corporation of Pennsylvania Application April 30,1941, Serial No. 391,104

7 Claims.

Our invention relates to railway signaling systems and particularly to asystem for the control of signals on stretches of single track overwhich traic normally moves in both directions.

In the signaling systems employed ori-stretches of track over which tracmoves in both directions it is necessary for a train to control thesignals in its rear to warn following trains, and to also control thesignals in advance of itself to warn an approaching train of itspresence.

The standard practice in absolute permissive block signaling systems isto arrange the equipment so that when a train advances beyond a passingsiding, all of the signals in the track stretch between that siding andthe adjacent siding in advance and controlling movement of trains in theopposite direction are caused to display their stop indications tothereby prevent a train moving in the opposite direction of trafc fromadvancing beyond the exit end of the adjacent passing siding.

In addition, it is customary in signaling systems of this type toarrange the signals governing each direction of traino so that when theheadblock signal at the exit end of a passing siding is displaying itsstop indication, the signal at the entrance end of the siding willdisplay a caution indication, and so that the adjacent signal in therear thereof will also display a caution indication. This control f thesignals is desirable so that when trains moving in opposite directionsapproach a passing siding at the same time, they will have ample warningof the approach of each other and will be able to stop before collidingeven though the passing siding is relatively short.

In the systems heretofore known the signals have operated in the manneroutlined above both when the headblock signal at the exit end of asiding is caused to' display its stop indication because a train movingin the direction opposite to that controlled by that signal isapproaching the signal, and when the signal is caused t0 display itsstop indication because a train moving in the direction of trafficcontrolled by that signal is immediately in advance of the signal. v

This method of operation of the signals is desirable Where two trainsmoving in opposite directions are approaching a passing sidingas itprovides the relatively long braking distance necing does not require asmuch braking distance as l is necessary when two trains moving inopposite directions are approaching each other.

If the signals operate as described above when two trains traveling inthe same direction are in the vicinity of a passing siding, the secondor following train will be given a caution indication sooner than isnecessary and the train will unnecessarily reduce its speed. l

It is an object of this invention t0 provide an improved signalingsystem of the type described which operates so that a train approachinga passing siding will receive a restrictive indication at a point lessdistant from the rear of a train moving in the same direction than fromthe front of a train traveling in the opposite direction, to therebyprovide ample braking distance for trains moving in opposite directionsWhile not unnecessarily retarding the second or following one of twotrains.

A further object of the invention is to provide an improved signalingsystem of the type described which is arranged so that signals for eachdirection of traflic are controlled so that when the headblocksignal atthe exit end of a passing siding is displaying its stop indicationbecause a train traveling in the opposite direction is approaching thesignal, the first and second signals in the rear thereof will displaytheir most restrictive proceed indications, and so that when theheadblock signal is displaying its stop indication because a traintraveling in the direction of traic controlled by that signal is inadvance of the signal, the adjacent signal in the rear will display itsmost restrictive proceed indication, but the second signal in the rearwill display a less restrictive indication.

Another object of the invention is to provide a signaling system of thetype described and which is arranged so that a minimum of line wires arerequired to obtain the desired .control of the signals.

Other objects of the invention and features of novelty will be apparentfrom the following description taken in connection with the accompanyingdrawings.

We shall describe two forms of apparatus embodying our invention, andshallthen point out the novel features thereof in claims.

In the drawings,

Fig. 1 is a diagram of a stretch of railway track equipped with one formof signaling system embodying our invention, and

Fig. 2 is a diagram showing a modified form of system embodying ourinvention.

Similar reference characters refer to similar parts in each of the twoviews.

Referring to Fig. 1 of the drawings, there is shown therein a stretch ofsingle track railroad over which traffic moves in both directions. Tofacilitate description of the equipment it will be assumed that theright-hand end thereof is east and that the left-hand end thereof iswest. Accordingly, train movements from left to right are eastbound, andtrain movements from right to left are westbound.

The track stretch includes passing sidings which are located atappropriate intervals and permit traliic to be diverted from the maintrack under the customary control of switches. One such passing sidingis shown in the drawings. The switch at the left or west end of thesiding is designated AW, while the switch at the right or east end ofthe passing siding is designated BW.

The rails of the track stretch are divided by insulated joints 3 intosuccessive track sections designated IGT, IIT, 12T, etc. Each of thesetrack sections is provided with a track circuit including a trackbattery connected across the section rails at one end of the section,and a track relay, designated TR with a suitable prex, connected acrossthe section rails at the other end of the section.

Eastbound trafc through the track stretch is governed by a plurality oftrackway signals designated'l 2S, 4S, GS, etc., while westbound trafficthrough the track stretch is governed by a plurality of trackway signalsdesignated IS, 3S, S, etc.

The signals shown in the drawings are of the color light type, but itshould be understood that the invention is not limited to the use ofsignals of this type and that any appropriate form of wayside signalswell known in the art may be employed.

Exceptl as hereinafter explained in detail, each of the signals has agreen or clear lamp G, a yellow or caution lamp Y, and a red or stoplamp R. The signals at the entrance ends of the passing sidings haveupper portions which include the green, yellow and red lamps asillustrated in the drawings, while these signals may also have lowerportions, not shown, governing movement of trains from the main trackonto the passing siding.

The signals next in the rear of the signals at the entrance endsof thepassing sidings include two red lamps and two green lamps as well as ayellow` lamp so as to be capable of displaying a clear signal comprisinga green over a red lamp, an approach medium indication comprising ayellow over a green lamp, a caution indication comprising a yellow overa red lamp, and a stop indication comprising a red over a red lamp.

The diagram which forms Fig. 1 of the drawings shows the means forcontrolling the signals which govern eastbound traffic including themeans for controlling the signal 2S. In order to simplify the disclosurethe means for controlling the signals` which govern westbound trafc hasnot been shown, but it should be understood that this equipment issubstantially the same as that shown for the eastbound signals.

The means for controlling the signal 2S includes line circuits I, II andIII. The line circuit I extends from the signal 2S to a point in advanceOf the west end of the passing siding, while the line circuit II extendsfrom the signal 4S at the west end of the passing siding to a point inadvance of the east end of the passing siding. The line circuit IIIextends from the signal SS eastward and is controlled in the manner Wellknown in the art by traffic conditions in the track stretch between theeast end of the passing siding shown and the adjacent passing siding inadvance. The supply of energy to the line circuit III may be controlledin the manner shown in United States Patent No. 1,294,736 to Sedgwick N.Wight.

The line circuits I and II are controlled in the manner hereinafterexplained in detatil so that at times both direct and alternatingcurrent energy is supplied over these circuits.

The track stretch is provided at appropriate locations with sources ofdirect current the terminals of which are designated B and C, while asource of alternating current having terminals BX and CX is provided.

The equipment is shown in the condition which it assumes when the trackstretch is vacant, and when the switches AW and BW are positioned todirect traffic through the main track.

At this time as the track stretch is vacant, energy of normal relativepolarity is supplied over the line circuit III to the relay BHD and theneutral contact and polar contact 2| of this relay establish the circuitof the green lamp G of signal GS.

In addition, at this time neutral contact 23 establishes a circuit tosupply energy to the pole changing relay SPC and the contacts 25 and 26of this relay are picked up.

As track section I4T is vacant, the track relay I4TR is picked up andits contact 28 interrupts the circuit of the eastbound directional stickrelay SES and thecontacts 30, 3| and 32 of this relay are released. Ascontact 32 is released, it interrupts connection from the secondarywinding of transformer LT to the line circuit 1I and establishesconnection from one wire of line circuit II to terminal C of a source ofdirect current.

At this time the westbound directional stick relay 3WS is released sothat connection is established from terminal B of the source of directcurrent through back contact 34 of relay SWS, front contact 35 of trackrelay ISTR, and front contact 36 of track relay MTR to the other wire ofline circuit II. Accordingly, energy is supplied to line circuit II, andas relay BPC is picked up, this energy is of normal polarity. Thisenergy feeds to the relay 4HD as track relays I3'IR and I2TR are pickedup, and as switch controlled contact AWN is closed. 'I'he contact AWN isclosed when and only when the switch AW is in its normal position.

As a result of the supply of energy of normal polarity to the relay4I-ID, neutral contact 38 and polar contact 39 cooperate to establishthe circuit of the green lamp G- of signal 4S, while neutral contact 40partially establishes the pickup circuit of eastbound directional stickrelay 4ES. In addition, neutral contact 42 and polar contact 43 of relay4HD cooperate to establish the circuit of the pole changing relay 4PC,while neutral contact 45 and polar contact 46 cooperate to establish acircuit short circuiting the primary winding of the transformer MT. Thisprevents inductive discharges of current from the transformer on releaseof the track relays governing line circuit I and thus reduces arcing atthese contacts.

At this time one wire of line circuit I is connected through thesecondary winding of transformer MT to terminal C of a source of directcurrent', While the other Wire of this line circuit is connected throughfront contact 48 of relay I3TR and front contact 49 of relay I2TR toterminal B of the source of current so that direct current energy issupplied to the line circuit I. As the contacts 50 and 5I of relay 4PCare picked up, the energy supplied to the line circuit I is of normalpolarity. This energy feeds to the relay 2HD and the neutral contact 53and polar contact 54 of this relay cooperate to partially establish thecircuit of the upper green lamp G of signals 2S, while neutral contact55 connects the primary Winding of transformer NT across the wires ofline circuit I. This circuit includes a resistor RA in series therewithto limit flow of direct current in the circuit of the transformerprimary winding. At this time alternating current is not supplied to theline circuit I so that no energy is supplied through the transformer NTand the associated rectier to the relay 2CD and the contacts of thisrelay are released. As the contacts 51 and 58 of relay 2CD are released,contact 51 establishes the circuit of the upper green lamp G of signal2S, while contact 58 establishes the circuit of the lower red lamp R ofsignal 2S. Accordingly, the signal 2S displays its clear indicationwhich consists of a green over a red lamp.

Operation of equipment on movement of an eastbound train through thetrack: stretch Release of contact 53 of relay 2HD interrupts the circuitof the upper green lamp G of signal 2S and establishes the circuit ofthe upper red lamp R so that the signal 2S displays its stop indicationconsisting of a red over a red lamp.

When the train advances into section IIT, the track relay II'IR releasesand additionally interrupts the line circuit I1 while when the trainenters section IZT, track relay I2I'R releases and interrupts linecircuits I and II. When line circuit II is interrupted, relay 1I-ID isdeenergized and its neutral contacts release s o that contact 38interrupts the circuit of the green lamp G of signal 4S and establishesthe circuit of the red lamp of this signal.

In addition, on release of the neutral contacts of relay 4I-ID contact42 interrupts the circuit of the pole changing relay IPC and thecontacts 50 and 5I of this relay release so that on the subsequentsupply of energy to the line circuit I the energy supplied to the relay2HD is of reverse relative polarity.

When the train enters section I2T, track relay I2TR releases and itscontact 59 establishes the pick-up circuit of the eastbound directionalstick relay 4ES. This circuit includes front contact 40 of relay MHD.However, the track relay IZTR is of a type which is relatively quick torelease, while the relay llHD is of a type the neutral contacts of whichare slow to release so that the l pick-up circuit of relay #IES ismomentarily cornplete. During this-period energy is supplied to therelay 4ES and its contact 62 picks up and establishes a stick circuitincluding backy contact 59 of track relay IZTR and front contact S2 ofrelay ISES for the relay winding, while another stick circuit for relayIES is established on release of contact 4U of relay Ill-ID.

OnV picking up of the4 contacts of relay -IIES contact 63 establishes acircuit shunting contact G8 of relay I3TR so that direct current energyis supplied to line circuit I as soon as the eastbound train vacatessection I2T.

When the train advances into section IST, track relay ISTR releases andadditionally interrupts line circuit II.

When the rear of the train vacates sections IIlT and IIT, the trackrelays IIITR and IITR pick up, butcontact 49 of track relay IZTR,vcontinues to interrupt line circuit I. When section IZT is vacated,track relay IZTR picks up and connection is established from terminal Bof the source of current through front contact A9 of relay IZTR, andfront Contact 63 of relay lES to one wire of line circuit I, While theother wire of this line circuit is connected to terminal C of the sourcethrough the secondary winding of transformer MT.

At this time the contacts of relay IPC are re'- leased so that theenergy supplied over line circuit I to the relay ZHD is of reversepolarity. On the supply of this energy to the relay ZI-ID its neutralcontacts pick up, while its polar contact 54 is shifted to itsright-hand or reverse position. As a result of 'picking up of contact 53and movement of contact 55, the supply of energy to the upper red lamp Rof signal 2S is cut off, while the circuit of the upper yellow lamp Y ofSignal 2S is established. v The signal, therefore, displays a yellowover a red lamp, which provides the caution indication.

As a result of energization of relay ZHD, contact 55 establishes thecircuit' of the transformer NT, but alternating current energy is notsuppliedl to the line circuit I at this time so that relay 2CD remainsreleased.

When the train advances into section If'lT,

track relay IQTR' releases and its contact 23 establishes the pick-upcircuit of eastbound directional stick relay SES so that the contacts ofthis relay pick up. Also, upon the release of track relay MTR, itscontact 52 opens line circuit III and d'eenergizes relay BHD. Theneutral contacts of relay 6R33 are slow releasing so that the pick-upcircuit of relay BES will be closed long enough for its front contact 39to close. Upon the closing of front contact 3B of relay BES, a stickcircuit including, back contact 23 of relay MTR is effective and uponthe closing of back Contact 69 of relay iii-ID, a second stick circuitis closed which keeps relay EES energized while an eastbound train is inthe block of signal 5S.

When the train enters section I5T, track relay IEE'IR releases andadditionally interrupts line circuit III.

As a result of picking up of the contacts of relay SES, contact 32establishes connection from terminal C of the source of direct currentthrough the secondary Winding of transformer LT to one Wire of linecircuit II, while Contact 3l partially establishes connection betweenterminal B and the other wire of line circuit II. This connection doesnot become complete until the train vacates section IAT and track relayMTR picks up and isY traced from terminal B through back contact 34 ofrelay SWS, front contact 3l of relay BES, and front contact 36 of trackrelay MTR.

Accordingly, when section |4T is vacated, direct current is supplied toline circuit II, and this energy is of Ireverse polarity as the relayBPC is released, while alternating current is also supplied to linecircuit II as the secondary winding of transformer LT is included inseries with the line circuit.

On the supply of direct current of reverse polarity to relay 4HD itsneutral contacts pick up, While its polar contacts are shifted fromtheir left-hand or normal positions to their right-hand or reversepositions. At this time the primary winding of transformer MT isconnected across` the wires of line circuit II by a circuit which istraced from one line wire through resistor RB, reverse polar contact 45,and front neutral contact 45 of relay 4HD to one terminal of the primarywinding of transformer MT, the other terminal of which is connected tothe other line wire of line circuit II. Accordingly, alternating currentsupplied to the line circuit II is supplied through the transformer MTto the line circuit I, while resistor RB substantially prevents flow of-direct current in the transformer primary winding.

When track relay I3TR picks up, its contact 48 is closed to establishconnection from terminal B of the source of direct current to one wireof line circuit I after release of contact 63 of relay 4ES. On pickingup of contact 40 of relay 4HD the stick circuit of relay 4ES isinterrupted and its contacts 62 and 53 release.

At this time contact 43 of relay 4HD is in its reverse position so thatenergy is not supplied to pole changing relay 4PC even though contact 42is picked up. Accordingly, the direct current energy supplied to relayZHD continues to be of reverse relative polarity.

As a result of the supply of alternating current energy to the linecircuit I, energy is supplied through the transformer NT and theassociated rectifier to the relay'2CD and the contacts of this relay arepicked up to thereby maintain the upper yellow lamp lighted whileextinguishing the lower red lamp and lighting the lower green lamp. Thesignal 2S, therefore, displays its approach vmedium indicationconsisting of a yellow over a green lamp.

At this time as neutral contact 38 of relay 4HD is picked up and polarcontact 39 of this relay is in its right-hand or reverse position, theyellow lamp Y of this signal is lighted to provide the cautionindication.

It will be seen, therefore, that as soon as th eastbound train vacatessection 12T, signal 2S is-conditioned to display its caution indication,and that when the train vacates section WI', signal 4S is conditioned todisplay its caution indication, while signal 2S is conditioned todisplay its approach medium indication.

Accordingly, a second or following train will receive an indication oftraic conditions in advance from signal 2S, but will not be required togreatly reduce its speed until it reaches signalllS at which point itwill receive a caution indication. 'Ihe second or following train,therefore, will not unnecessarily reduce its speed at signal 2S, butwill continue until it reaches 4S, while after reaching signal 4S thetrain will have sufcient distance in which to stop without running intothe rear of the preceding train. At this time the braking distancerequired by the second train is determined only by its own stoppingdistance since the preceding train is moving in `the same direction, oris standing still, and the two trains are not approaching each other.

When the first train advances beyond signal 8S, this signal is caused todisplay its stop indication, while energy of reverse relative polarityis supplied by means not shown to the line circuit III so that when thetrain vacates sections IST and IST, this energy feeds to the relay 61m.As a result, neutral contact 20 and polar 4contact 2| establish thecircuit of the yellow or caution lamp Y of signal GS, while contact 23establishes the circuit of the relay GPC. In addition, contact 60 ofrelay BHD interrupts the holding circuit of relay BES and the contactsof this relay release.

On release of contact 32 of relay BES one wire of line circuit II isconnected directly to terminal C of the source of direct current insteadof being connected through the secondary winding of transformer LT.Accordingly, the supply of alternating current to the line circuit II iscut olf, and energy is no longer supplied through the transformer MT toline circuit I and to the relay 2CD so that the contacts of this relayrelease.

At this time the other wire of line circuit II is connected to terminalB of the source of current through front contact 36 of track relay MTR,front contact 35 of track relay I5TR, and back contact 34 of directionalstick relay 3WS so that energy is supplied to line circuit II and torelay 4HD. As the contacts of relay GPC are picked up, the energysupplied to the relay 4HD is of normal relative polarity and polarcontact 39 of relay 4HD is shifted from its reverse to its normalposition to thereby extinguish the yellow lamp Y and light the greenlamp G of signal 4S.

In addition, at this time polar contact 43 of relay 4HD establishes thecircuit of the relay 4PC, while polar contact 45 establishes the circuitto short circuit the primary winding of transformer MT. As relay lPC isenergized, the energy supplied to relay 2HD is changed from reverse tonormal polarity and contact 54 is shifted from its reverse to its normalposition, while at this time relay 2CD is released as explained above.Accordingly, the upper green lamp G and the lower red lamp R of signal2S are lighted so that this signal provides its clear indication.

When the train advances beyond the signal next in advance of signal 8S,the energy supplied to relay GHD is changed from reverse to normalpolarity so that contact 2| interrupts the circuit of the yellow lamp Yand establishes the circuit of the green lamp G of signal GS, whilecontact 23 maintains the circuit of relay SPC so that energy of normalpolarity is supplied to line circuit II and signals 4S and 2S continueto display their clear indications.

Operation of system on movement of a westbound train through the trackstretch 'When a westbound train leaves the passing siding next in theeast of the siding shown, the supply of energy to the line circuit IIIis cut off in the manner well known in the art.

As a result of deenergization of relay BHD, contact 20 establishes thecircuit of the red lamp R of signal SS to prevent an eastbound trainproceeding beyond the passing siding. In addition, on release of relayGI-ID Contact 23 interrupts the circuit of the relay BPC so that itscontacts release and change the polarity of the energy supplied overline circuit II fronrnormal:

to reverse. On release of.' contact 60pt relay BHD ther pick-up circuitof eastbound directionall stick relay SES is interrupted andy contactsA3l. and 32 of this relay remain released so that:

alternatingI current energy is notv supplied tcthe line circuit II.

At this time one line Wire of line. circuit II: is connected to terminalB of the sourcethrough` front contact 3% of track relay MTR, frontcontact 35 of track relay l5TR,.and back contact,

34 of directional relay SWS, While the other line wire of line circuitII is connected through back contact 32 of relayx GES to terminal C.'so. that relay HD is energized and its polar.l con tact Sil-establishesthe circuit of the yellow lamp Y of signal iS.

of relay iHD connects the primary winding of transformer MT acrossthe-Wires of line circuit II, but as alternating current is notbeingsupplied to line circuit II, no energy is supplied through thistransformer to the line circuit I' and relay 2CD remains released. Asrelay 2CD is released and relay ZHD is supplied with energy of reversepolarity, the upper yellow lamp Y and the lower red lamp R of signal 2Sare lighted so that signal 2S pro-vides its caution indication.

It Will be seen, therefore, that when a Westbound train is approachingthe passing siding,

signal S displays its stop indication, Whilesig- Ac cordingly, aneastbound train Will begin to renals 4S and 2S display cautionindications.

duce its speed when it reaches signal 2S and will have adequate space inwhich to stop before colliding with the Westbound train, even if thewestbound train should continue beyond signal 3S before stopping.

When the westbound train enters section IST, contact 35 of track relayI5TR releases and interrupts line circuit II to thereby cut on thesupply of energyto relay :ti-ID.

On interruption of the supply of energy to y,

the relay HD the neutral contacts of this relay release and contact 38establishes the circuit of the red or stop lamp R of signal 4S. Releaseof relay fil-ID does-not aiect the supply of energy` to line circuit Iand energy of reverse polarity continues to be supplied to the relay ZHDso that the signal 2S continues to display its caution indication.

When the Westbound train under consideration advances into section MT,track relay MTR releases and its contact (i5 establishes the pick-up.

cir-cuit of the Westbound directional stick relay 3WS. This circuitincludes front Contact 66 of relay BHD which controls the signal 3S intheV same manner that relay lll-ID controls signal 4S. On the supply ofenergy to relay SWS itscuit II and to relay HD is additionally inter-Yrupted.

When the westbound train' enters section HiT, contact 28A of relay MTR.is released, but at In addition, polar contact is? interrupts thecircuit of relay liPC so that energy. of reverse polarityis suppliedover line circuit I torelay ZI-ID. At this time polar contact if this.time theY pick-up circuit of relay SES is interruptedlby contact GOLoffrelay SI-IDrsothat' rela-yf GESremains released.

Whenthe Westbound train enters section.l3T, trackV relay ISTR.V releasesandl its contactv 48'. interrupts the supply of energy to linecircuit I.so: that relay 2I-ID. releases and contact 53 establishes the circuitof.` the upper'. red lamp Rzof'isignal 2S.` This signal,therefore,.dis1: laysl ared. lamp over a redlarnptoiprovide the stopindication.

If; the westbound train. continues beyond signal. 5S, track relay.` IZTRWillrelease andinf terrupt line circuitLI,` Whilefin similar, mannerytrack relays HTR and ISTR Will release. when` the train enters; these.-sections. These. track relays, interruptr line circuit I: andthus, causesignal 2S to continuato; display itsestopgindifcation*- From theforegoingitzwill be seen tlfiatvvhen a train traveling in` onedirectionadvances'beyOIld,l a passing siding, the signals in the rear ofthat'train and controlling train movements in that'` directionare governed insuch manner; that the signal at the entrance end of the passing sidingWill display its caution indication, While the adjacent signal in therear thereof will display itsapproach medium indication. rIhis providesa followingV train with a Warning of theV presence of` the rst trainwithout requiring the following. train to reduce its speed before it isnecessary to do so.

On the other hand, when a train moving in one direction is approachingthe passingsiding, the signals governing movement of trains inthe otherdirection are controlled in such manner that the signal at the other endof the passing siding` and the signal next in the rear thereofboth-display caution indications so that a second train moving in saidother direction Will have ample warning ofv the-presence-of the'rsttrain andV will stop beforerclliding With'that train.

It will be seen also that the control ofA the signals isarranged-in suchmanner that aminimum'r of' line Wires are required since the approachmedium signal indication is provided by superimposing alternatingcurrent on the existing line circuits.

Construction of system shown in-Fig; 2

In Fig. 2 of thefdrawingsthere is: shown a modied system for securingthe same control of thefsignals as is provided bythe systemshown in Fig.1.

The system show n inFig. 2is similar tol that shown in Fig. 1, and.diiers therefrom in that coded energy instead of alternating currentenergy is supplied to the line circuits4 aty times toprovide anadditional proceed indication..

The equipmentis shown in Fig. 2 in the-condition which it assumes whenthe track stretch is Vacant. At this time direct current energy issupplied over line circuit III to relay GHD so that contacts 20 and 2lof this relay establish thecircuit of the green lamp G of signal GS.,

At thistime contact 2.8 of track relay MTR interrupts the circuity ofveastbound directional stick relay GES so that contacts` 3l and 32 arereleased. Contact 32, therefore, interrupts the circuit of codetransmitter HCT and this device is deenergized; Contact` 3`I ofrelay ES.establishes connectionirom one Wire of line circuit II` to terminal Cof` a.source of direct current, while the other Wire of this linecircuit is connected through contact 36 of relay MTR, Contact 35- ofrelay WTR.,V and contact 34 of relay 3WS to terminal B of the source sothat energy is supplied to line circuit II. This energy is of normalrelative polarity as the pole changing relay BPC is energized by currentsupplied over contact 23 of relay ISI-ID.

The energy supplied to the line circuit II feeds tc the relay 4HD andcontacts 38 and 39 of this relay cooperate to establish the circuit ofthe green lamp G of signal 4S, While contacts 42 and 43 cooperate toestablish the circuit of the pole changing relay 4PC. As contact 42 ofrelay 4HD is picked up, the circuit of the primary Winding of decodingtransformer IDT is interrupted and the relay 4H is released. Inaddition, contact 'I0 Vof relay 4HD interrupts the circuit of the relay4CR, while contact 1I interrupts the circuit of the code transmitterICT.

At this time one Wire of line circuit I is connected to terminal C of asource of direct current through front contact 5I of relay 4PC and frontcontact 'I2 of relay 4HD, while the other Wire of line circuit I isconnected through front contact 5D of relay 4PC, front contact 'I3 ofrelay 4HD, front contact 48 of relay I3TR, and front contact 49 of relayIZTR to terminal B of the source. Accordingly, energy is supplied to theline circuit I, and as the contacts of relay 4PC are picked up, thisenergy is of normal relative polarity and the relay 2HD is energized.

At this time, therefore, contact 'VI of relay 2HD interrupts the circuitof the code following relay 2CR, While contact I8 interrupts the circuitof the primary Winding of decoding transformer 2DT and establishes acircuit to energize a relay 2DP. As relay 2DP is energized, its contact3i] is picked up and cooperates with the polar contact 54 of relay 2HDand contact 5I of relay 2H to establish the circuit of the upper greenlamp G of signal 2S, while contact 58 of relay 2H establishes thecircuit of the lower red lamp R of signal 2S.

Operation of system shown in Fig. 2 on movement of an eastbound trainthrough the track stretch When an eastbound train, that is a trainmoving from left to right, enters section `T, the track relay IDTRreleases and interrupts line circuit I so that relay 2HD releases andits contact 'I8 interrupts the circuit of relay 2DP. Accordingly,contact 8E! of relay 2DP releases and establishes the circuit of theupper red lamp R of signal 2S to thereby condition this signal todisplay its stop indication.

When the train advances into section I IT, the track relay IITR releasesand additionally interrupts line circuit I, while when the train entersnects the relay 4CH/across the line circuit II. As line circuit II isinterrupted by track relay I2TR, the relay 4CR remains released, Whileas section IZT, track relay IZTR releases and interrupts line circuitII, and its contact 49 interrupts line circuit I. In addition, contact`59 of relay I2TR establishes the pick-up circuit of eastbound stickrelay 4ES so that contact 62 of relay 4ES picks up and establishes astick circuit for the relay 4ES. The pick-up circuit is interrupted onrelease of contact 40 of relay 4HD, but release of contact 4testablishes another stick circuit for relay 4ES.

As a result of interruption of line circuit II, relay 4HD releases andits contact 38 establishes thecircuit of the red or stop lamp R ofsignal 4S. This circuit includes, in addition; back contact 82 of relay4H. On release of relay 4HD contact 42 interrupts the circuit of relay4PC and establishes the circuit of the primary winding of the decodingtransformer 4D'I, While contact 'I0 conrelay 4PC is released, itscontact 59 interrupts the circuit of code transmitter ICT.

The code transmitter ICT has a contact Which when the device isenergized is alternately opened and closed at a rate such as to providea number of energy impulses each minute, such as '75 a minute, Which areseparated by periods of equal duration in which no energy is supplied.While the supply of 75 energy impulses a minute is mentioned, this isillustrative only and any desired frequency of energy impulses may beernployed. 'j'

When the train advances into section I3T, track relay I3TR releases andadditionally interrupts line circuits I and II, While when the trainenters section I4T, track relay I4TR releases and its contact 28establishes the pick-up circuit of relay GES so that its contacts 3| and32 pick up and contact 36 of relay MTR interrupts line circuit II. As aresult of picking up of contact 32, the circuit of the code transmitterIICT is established, While contact 3| establishes connection from oneline wire of line circuit II through code transmitter contact 'I5 toterminal C of the source. At this time, however, connection from theother Wire of the line circuit to terminal B is interrupted by contact36 of relay I4TR so that energy is not supplied to the line circuit.

On release of relay MTR its contact 2'8 establishes the pick-up circuitof relay GES and contact 30 of relay SES thereupon picks up andestablishes a stick circuit for the relay.

In addition, on release of track relay I4 TR its contact 52 interruptsline circuit III so that relay BHD releases and its contact 60interrupts the pick-up circuit and establishes the stick circuit forrelay 6ES to thereby insure that relay 'SES Will remain energized aftercontact 28 of relay MTR is picked up.

As a result of release of relay BHD, contact 20 establishes the circuitof the red or stop lamp R of signal GS, while contact 23 releases andinterrupts the circuit of the relay SPC.

When the train vacates section I2T, track relay IZTR picks up andestablishes a circuit for supplying energy to the line circuit I. Atthis time one wire of this line circuit is connected through backcontact 50 of relay 4PC to terminal C, While the other Wire of the linecircuit is connected through back contact 5I of relay 4PC, front contact63 of relay 4ES, and front contact 49 of relay IZTR to terminal B of thesource. Accordingly, energy is supplied to line circuit I, and theconnections are arranged so that the energy supplied to the relay 2HD isof reverse polarity. On picking up of relay 2HD a circuit is establishedto energize the relay 2DP so that its contact 8D picks up, while polarcontact 54 is shifted to its reverse position with the result that theupper red lamp R of signal 2S is extinguished and the upper yellow lampY is lighted to thereby cause this signal to display its yellow over redor caution indication.

When the train vacates section IST, the track relay ISTR picks up, butline circuit II continues to be incomplete until track relay MTR ispicked up. When the train vacates section MTR, connection is establishedfrom one Wire of line circuit II through front contact 36 of track relayI4TR, front contact 84 of relay SES, and back contact 34 of relay SWS toterminal B, while the other Wire of the line circuit II is connectedagar-rai throughggfront contact S'lofl relay GES and code transmittercontact 'l5 to terminal C so that im'- pulses off' coded energy are'supplied to the line circuit II.

The coded' energy supplied to' line circuit II feedsA t'othe relays GHDand 4CH.;v The relay 4'IlfD'is-of'-` a'f-typev which is relatively slowacting withlthe result that itsneutral contacts remainV released whencoded energy is supplied to the relay. The coded energyr supplied torelay ACR produces code following operation of the relay energy issupplied through thev decoding transformer DT to the relay 4H, andcontacts 841V andiSEof vthis relay-are picked up so thatcontact'tflestablishesthe circuit of the relay liPC, while contact 8-2interrupts the circuit of the red lamp Rand establishes the circuit ofthe yellow lamp Y- of; signal 4S. Accordingly, the signal 'iS displaysVits caution indication when the train clearssection .l ITIL On the.supply of. energy to relay APC thecontactszofs this relay'pickf up sothat the circuit traced above for supplying energy`V to line circuitItis interrupted, while a circuitin'cluding contact 15? of codetransmitter ICT is established to supplyenergy to the line circuit I.This circuit is complete'as'- one. wire of line circuit I is connectedthrough front contact 5e. of relay 41C, back'vc'ontact 13' of relayI-ID, and. code transmit'tercontact 'l'to terminal C, while the otherline` wire is.- connected. through. front contact 5i ofrelay lPC; backcontact'lZ of relay I-ID, front contact 1.458V of-relay ISTR, and frontcontact igor relay IZTR to terminal B of the source of current.Accordingly, coded energy is supplied to linecircuit I. The relay ZHD,like the relay I-ID, is immune to coded energy and its contactsbecornereleased at this time and establish the circuit of the relay 2CRso that relay ECR, responds to the coded energy supplied to the linecircuit and energy is supplied through the decoding transformer 2DT tothe relay 2H.

On picking up of the contacts of relay. 2H itsy contact 82 establishesacircuit to energize relay low lamp Y of signal 2S lighted and contact53 picks up to interrupt the circuit of the lower red lamp and establishthe circuit of the lower green i lamp.V Accordingly, when the eastboundtrain vacates section MT, the signal 2SV displays itsapproach mediuminstead of its caution indication.

When the eastbound train vacates section SGT,

energy of reverse relative polarity is supplied` over line circuit IIIto relay @HD andits contact Si) picks up and interrupts the stickcircuit of relay SES so that contacts 3l and 32 of this relay release.Release of contact 32 interrupts the circuit of code transmitter IICI,while release of contact 3i interrupts the circuit of the codetransmitter contact and connects one wire of the line circuit II toterminal C of the source. At this time the other wire of the linecircuit II is connected through contact 33 of relay MTR, Icontact 35 ofrelay I5TR, and back contact 34 of relay 3WS to terminal B of thesource, while contact 23 of relay @HD establishes the circuit of thepole changing relay SPC so that energy of normal relative polarity isnow supplied to the line circuit II. In addition, as a result oflenergization of relay, @HD with energy oflreversepolarity, the contacts2Q and 2i osthisA relay cooperate to establish.V the circuit of the.

yellow lamp Y of signalA G'S so that thissig'nal provides its cautionindication'.

On the supply-of? energy ofi normalpolarity to line -circuitI-IIthe-neutralfcontacts of relay 4HD pick up-- and` contacts 33 and 39 ofthis relay cooperate tol establish the circuit of the green lampCtofsignal 4S, whilec'ontactAZ interrupts the circuiti oi`4v decodingtransformer 4D? andl contacts rl'and i3r cooperate to establisha-circuit?. to4 maintainf relay I#PCA energizedi In addition;V4 contactilinterrupts the stick circuit of the directional. stickl relay QES,while contact 'I I interrupts? the. circuit of the codev transmitterICT. and' contact. 10; interrupts the: circuit of the relayi'liCR.A'slthe. relay CR no longer follows code,1contact 8l" ofrelay'dHr'eleases, but energy is supplied to relay 4PC over contacts 42and 43 of relay tI-IDL On picking up of the contacts of relayv AHDcontact 'I3 interrupts the circuit of the*V codetransmitter contact 'l5and establishes connectionrfrom' onefwire of'line circuit I throughcontact 48' of track` relay ISTR and' contact #lg-of track: relay I'ZTRto terminal Bi of the sourcel of current; while contact 'I2 connects theother wire of the line circuit to terminal C. Accord'- ingly, steadyenergy is suppliedl to the line circuit I, while asthe contacts of relayIPC are picked up,V this energy is of normal polarity.

On the supply of this energy to relay ZHD its contacts" pick4 up andinterrupt the cir-cuit of therelay 2CR-,while relayZHreleases and polarcontact 54 is shifted to its normal position. Accordingly, thecircuits'of the upper'yellow and lowergreen lamps are interrupted andthe circuits oi the upper green and lower red lampsA are establishedsothat signal ZSagain-displays its clear signal.

Operation of systemV shown in. Fig. 2.011, movement ofan` westboundYtrain through theV track stretch.

Assuming thatthe track-stretch isotherwise gle track stretch at theright of-thepassing siding,.the"supply of energy to the line circuit IIIis cut oir and relay BHD releases and its'contact 2,0 establishes thecircuit ofA the red or stop lamp Rof signal ES, while its contact 23interrupts the circuit of the pole changing relay SPC so thatthe energyYsupplied to line circuit II is changedirom normal to reverse polarity.

On this change in the energy suppliedto relay dI-ID'thepolar contacts ofthis relay are shifted tortheirI reverse positions and contacts 38 and39 'establish the circuit of` the yellow lamp Y of signalJiS. Inaddition, at this time contact 43 interrupts the circuit of the polechanging relay APC and its contacts release andchange the polarityvof:the-energy supplied to line circuit I from` normal yto reverse.

As a result, `the polar contact 5ft` of relay 2HD is shifted to itsreverse position to thereby eX- tinguishlthe upper green lamp and lightthe upper` yellowy lamp Y of signal 2S', while the lower red lamp R ofthissignal remains lighted to cause the signal to display its vcautionindication.

`It will be seen, therefore, that when a Westbound `train is approachingthe passingsiding, the signal-atthe opposite end of the siding andgoverning traiiic in the opposite direction, as

well as the adjacent signal inthe rear thereof displaycautionindications. Accordingly, an eastbound train approaching thepassingsiding will 4hayetample warningof. the approach of-thewestbound trainand will be able to stop beforer colliding with the westbound train.

When the westbound train enters section T, track relay I5TR releases andits Contact 35 interrupts line circuit II so that the supply of energyover line circuit II is cut oft and relay 4HD releases and its contact38 establishes the circuit of the red or stop lamp R of signal 4S. Atthis time energy of reverse relative polarity continues to be suppliedto line circuit I so that signal 2S continues to display its cautionindication.

When the westbound train advances beyond signal 3S, track relay MTRreleases and relay 3WS is energized so that its contact 34 prevents thesupply of energy to line circuit II. The relay 3WS is controlled in amanner similar to relay 4ES.

When the westbound train advances into section I3T, track relay I3TRreleases and its contact 48 interrupts the supply of energy to linecircuit I and relay 2IID thereupon releases and interrupts the circuitof relay 2DP so that contact 8U of relay ZDP releases and establishesthe circuit of the upper red lamp R of signal 2S to thereby cause thissignal to display its stop indication.

It will be seen, therefore, that the system shown in Fig. 2, like thatshown in Fig. 1, is arranged so that when two trains traveling inopposite directions are in the vicinity of a passing siding, the signalsoperate to provide restrictive indications to insure adequate stoppingdistance for the trains, while when two trains traveling in the samedirection are in the vicinity of a passing siding, the signals operateto provide adequate warning of the presence of the first train withoutunnecessarily requiring the second train to reduce its speed.

Although we have herein shown and described only two forms of apparatusembodying our invention, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

l. In combination, a stretch of railroad track over which traffic movesin both directions, said track stretch including a passing siding, aplurality of signals governing movement of trains in one directionthrough said track stretch, said signals including a first signal at theexit end of the siding, a second signal at the entrance end of thesiding and a third signal in the rearof said secon-d signal, said rstand second signals being capable of displaying a clear, a caution and astop indication, said third signal being capable of displaying a clear,an approach medium, a caution and a stop indication, a iirst linecircuit substantially coextensive with said Vsiding and governed bytraic conditions in the track stretch adjacent said siding, a secondline circuit extending between the second and third signals and governedby traic conditions in the track stretch intermediate said signals,means governed by trafc conditions in the track stretch in advance ofthe rst signal and controlling the supply of energy to the first linecircuit, said means being operative when said stretch in advance of therst signal is vacant to supply energy of a first character to said linecircuit, when said stretch in advance of the rst signal is occupied by atrain moving in said one direction to supply energy of a secondcharacter to said first line, circuit, and

when said stretch in advance of the first signal is occupied by a trainmoving in the other direction to supply energy of a third character tosaid first line circuit, electroresponsive means receiving energy oversaid first line circuit and controlling said second signal and alsocontrolling the supply of energy to said second line circuit, saidelectroresponsive means being eiective on the supply thereto of energyof said rst character to condition said second signal to display itsclear indication and to effect the supply of energy of said rstcharacter to the second line circuit, said means being effective on thesupply thereto of energy of said second character to condition saidsecond signal to display its caution indication and to effect the supplyof energy of said second character to said second line circuit, andbeing effective when supplied with energy of said third character tocondition said second signal to display its caution indication and toeffect the supply of energy of said third character to said second linecircuit, said means being eective when deenergized to condition saidsecond signal to display its stop indication and to effect the supply ofenergy of said third character to said second line circuit, andelectroresponsive means receiving energy over said second line circuitand controlling said third signal so as to cause said signal to displayits clear, approach medium or fcaution indications according as energyof the iirst, second or third characters are supplied thereto and whenno energy is supplied to said means to cause said signal to display itsstop indication.

2. In combination, a stretch of railroad track over which traiiic movesin both directions, said track stretch including a passing siding, aplurality of signals governing movement of trains in one directionthrough said track stretch, said signals including a first signal at theexit end of the siding, a second signal at the entrance end of thesiding and a third signa] in the rear of said second signal, said rstand second signals being capable of displaying a clear, a caution and astop indication, said third signal being capable of displaying a clear,an approach medium,

f a caution and a stop indication, a first line circuit substantiallycoextensive with said siding and governed by traflic conditions in thetrack stretch adjacent said siding, a second line circuit extendingbetween the second and third signals and governed by traiic conditionsin the track stretch intermediate said signals, means governed by traicconditions in the track stretch in advance of the first signal andcontrolling the supply of energy to the first line circuit, said meansbeing operative when said stretch in advance of said first signal isvacant to supply direct current of normal polarity to said rst linecircuit and being operative when said stretch in advance of said rstsignal is occupied to supply direct current of reverse polarity to saidfirst line circuit, said means being operative when the train occupyingsaid stretch in advance of said rst signal is moving in said onedirection to also supply alternating current energy to said rst linecircuit, electrore'sponsive means receiving energy over said first linecircuit and controlling said second signal and also controlling thesupply of energy to said second line circuit, said electroresponsivemeans being effective on the supply thereto of direct current of norma1polarity to condition said second signal to display its clear indicationand to effect the supply of direct current of normal polarity to thesecond line circuit,

said means being effective on the supply thereto of direct current ofreverse polarity to'conditi'on said second signal to display its cautionindication and to effect the supply of direct current of reversepolarity to said second line circuit,V said means being effective whensupplied with alternating current to effect the supply of alternatingcurrent to said second line circuit, said means being effective when'deenergized to condition said second signal .to display its stopindication and to effect the supply of direct current of reversepolarity to said second line circuit, and electroresponsive meansreceiving energy over said second line circuit and controlling saidthirdsignal so as to cause said signal to display its clear, approach mediumor caution indications according as direct current of normal polarity,direct current of reverse polarity together with alternating current ordirect current of reverse polarity alone is supplied thereto, and whenno energy is supplied to said means to cause said third signal todisplay its stop indication.

3. In combination, a stretch of railroad track over which traffic movesin both directions, said track stretch including a passing siding, aplurality of signals governing movement of trains in one directionthrough said track stretch, said signals including a rst signal at theexit end of the siding, a second signal at the entrance end of thesiding and a third signal in the rear of said second signal, said firstand second signals being capable of displaying a clear, a caution and astop indication, said third signal being capable of displaying a clear,an approach medium, a caution and a stop indication, a first linecircuit substantially coextensive With said siding and governed by trafcconditions in the track stretch adjacent said siding, a second linecircuit extending between the second and third signals and governed bytraic conditions in the track stretch intermediate said signals, means4governed by traffic conditions in the track stretch in advance of therst signal and controlling the supply of energy to the first linecircuit,said means being effective when said stretch in advance of saidvfirst signal is vacant to supply direct current of normal polarity tosaid `first line circuit and being effective when said stretch inadva-nceof the first-signal is occupied to supply direct current ofreverse polarity to said first line circuit, a directional stick relay,means effective when a train moving in said one direction 'enters saidtrack stretch in advance of said first signal to energize saiddirectional stick relay, said relay being effective When energized tosupply alterl nating current energy to said first line circuit,electroresponsive means receiving energy over said first line circuitand controlling said second signal and also controlling the supply ofenergy to said second line circuit, said electroresponsive means beingeffective when supplied with direct current of normal polarity tocondition said second signal to display its clear indication and toeffect the supply of direct current of normal polarity to said secondline circuit, saidV means being effective when supplied With directcurrent of reverse polarity to condition said second signal to displayits caution indication and to supply direct current of reverse polarityto said second line circuit, said means being also eiective whensupplied with alternating current to effect the supply of alternatingcurrent to said second line circuit, said means being effective whendeenergized to condition said second signal to display its stopindication and to supply direct current of reverse polarity to saidsecond line circuit, and electroresponsive means receiving energy oversaid second line circuit and controllingsaid third signal so as to causesaid signal to display its clear, approach medium or caution indicationsaccording as direct current of normal polarity, direct current ofreverse polarity together with alternating current or direct current ofreverse polarity alone is supplied thereto, and when no energy issupplied to said means to cause said third signal to display its stopindication.

4. In combination, a stretch of railroad track over which traffic movesin both directions, said track stretch including a passing siding, aplurality of ignals governing movement of trains in one directionthrough said track stretch, saidl signals including a first signal atthe exit end of the siding, a second signal at the entrance end of thesiding and a third signal in the rear of said second signal, said-firstand second signals being capable of displaying a clear, a caution and astop indication, said third signal being capable of displaying a clear,an approach medium, a caution and a stop indication, a first linecircuit substantially coextensive with said siding and governed bytraffic conditions in the track stretch adjacent said siding, a secondline circuit eX- tending between the second and third signals andgoverned .by traffic conditions in the track stretch intermediate saidsignals, means governed by traffic conditions in the track stretch inadvance of the first signal and controlling the supply of energy to thefirst line circuit, said means being effective when said stretch inadvance of said first signal is vacant to supply direct current ofnormal polarity to said rst line circuit and being effective when saidstretch in advance of the first signal is occupied to supply directcurrent of reverse polarity to said rst line circuit, a directionalstick relay, means effective when a train moving in said one directionenters said track stretch in advance of said rst signal to energize saiddirectional stick relay, said relay being effective when energized tolsupply alternating current to said first line circuit, a line relayreceiving energy over said rst line circuit and effective when suppliedwith direct current of normal polarity to condition said second signalto display its clear indication and to supply direct current of normalpolarity to said second line circuit, and When supplied with directcurrent of reverse polarity to condition said second signal to displayits caution indication and to supply direct current of reverse polarityto said second line circuit, said relay being also effective whendeenergized to supply direct current of reverse polarity to said secondline circuit, a transformer having its primary Winding connected toreceive energy from said first line circuit and its 4secondary windingconnected to supply energy to said second line circuit, andelectroresponsive means receiving energy over said second line circuitand controlling said third signal so as to cause said signal to displayits clear, approach medium, caution or stop indications according asdirect current of normal polarity, direct current of reverse polaritytogether with alternating current, direct current of reverse polarity orno energy is supplied to said means.

5. In combination, a stretch of railroad track over which traffic movesin both directions, said track stretch including a passing siding, aplurality of signals governing movement of trains in one directionthrough said track stretch, said signals including a first signal attheexit -end of the siding, a second signal -at the entrance end of thesiding and a third signal in the rear of said second signal, said rstand second signals being capable of displaying-a clear, a caution and astop indication; said third signal being capable of displaying a clear,an approach me-V dium, a caution and a stop indication, a first linecircuitI substantially coextensive with said siding and governed bytraiic conditions in the track stretch adjacent said siding, a secondline circuit extending between the second and third signals and governedby traiiic conditions in the track stretch intermediate said signals,means governed by trailic conditions in the track stretch in advance ofthe rst signal and controlling the supply of energy to the rst linecircuit, said means being effective when said track stretch in advanceof said rst signal is vacant to supply direct current of normal polarityto said rst line circuit and being eiective when said stretch in advanceof said rst signal is occupied to supply direct current of reversepolarity to said rst line circuit, said means being effective when thetrain occupying said stretch in advance of said rst signal is moving insaid one direction to alternately interrupt and establish the supply ofvenergy to said iirst line circuit to thereby cause the energy suppliedthereto to be coded, electroresponsive means receiving energy over saidfirst line circuit and controlling said second signal and alsocontrolling the supply of energy to said second line circuit, said meansbeing effective when supplied with steady current of normal polarity tocondition said second signal to display its clear indication and tosupply direct current of normal polarity to said second line circuit,said means being effective when supplied With steady direct current ofreverse polarity to condition said second signal to display its cautionindication and to supply steady direct current of reverse polarity tosaid second line circuit, said means being effective when supplied withcoded direct current to also condition said second signal to display itscaution indication and to supply coded direct current to said secondline circuit, and electroresponsive means receiving energy over saidsecond line circuit and controlling said third signal so as to causesaid signal to display its clear, approach medium, caution or stopindications according as steady direct current of normal polarity, codeddirect current, steady direct current of reverse polarity, or no energyis supplied to said means.

`6. In combination, a stretch of railroad track over which traffic movesin both directions, said track stretch including a passing siding, aplurality of signals governing movement of trains in one directionthrough said track stretch, said signals including a first signal at theexit end ot the siding, a second signal at the entrance end 'of thesiding and a third signal in the rear of said second signal, said firstand second signals being capable of displaying a clear, a caution and astop indication, said third signal being capable of displaying a clear,an approach medium, a caution and a stop indication, a rst line circuitsubstantially coeXtensive with said siding and governed by traiiicconditions in the track stretch adjacent said siding, a second'linecircuit extending between the second and third signals and governed bytraffic'conditions in the track stretch intermediate said signals, meansgoverned by traffic conditions in the track stretch in advance of thefirst signal and controlling the supply of energy to the lfirst linecircuit, said means being effective when saidV stretch in advance ofsaid rst signal is vacant to supply steady direct current of normalpolarity to said rst line circuit and being effective when said Stretchin advance of said i'lrst signal is occupied to supply direct current ofreverse polarity to said rst line circuit, a directional stick relay,means eiective when a train moving in said one direction enters saidtrack stretch in advance of said first signal to energize saiddirectional stick relay, said relay being operative When energized toinclude a contact of a coding device in the circuit for supplying codedenergy to said rst line circuit, electroresponsive means receivingenergy over said first line circuit and controlling said second signaland also controlling the supply of energy to said second line circuit,said electroresponsive means being effective when supplied with steadyenergy of normal polarity to condition said signal to display its clearindication and to supply steady energy of normal polarity to said secondline circuit, said means being eiective when supplied with coded energyto condition said signal to display its caution indication and to supplycoded direct current to said second line circuit, said means beingeffective when supplied with steady. direct current of reverse polarityto condition said second signal to display its caution indication andtosupply steady direct current of reverse polarity to said second linecircuit, said means being effective when deenergized to condition saidsecond signal to display its stop indication and to supply steady directcurrent of reverse polarity to said second line circuit, andelectroresponsive means receiving energy over said second line circuitand controlling said third signal so as to cause said signal to displayits clear, approach medium, caution or stop indications according assteady direct current of normal polarity, coded direct current, steadydirect current of reverse polarity or no energy is supplied thereto.

' 7. In combination, a stretch of railroad track over which trafc movesin both directions, said track stretch including a passing siding, aplurality of signals governing movement of trains in one directionthrough said track stretch, said signals including a rst signal at theexit end of the siding, a second signal at the entrance end of thesiding and a third signal in the rear of said second signal, said firstand second signals being capable of displaying a clear, a caution and astop indication, said third signal being capable of displaying a clear,an approach medium, a caution and a stop indication, a rst line circuitsubstantially coextensive with said siding and governed by traiiicconditions in the track stretch adjacent said siding, a second linecircuit extending between the second and third signals and governed bytraific conditions in the track stretch intermediate said signals, adirectional stick relay, means effective when a train moving in said onedirection enters said track stretch in advance of said first signal t0`energize said directional stick relay, means governed by saiddirectional stick relay and by traiiic conditions in said track stretchin advance of said first signal for supplying energy to said first linecircuit, said means being effective when said stretch in advance of saidfirst signal is vacant to supply energy of a rst character to said rstline circuit, when said stretch in advance of said first signal isoccupied by a train moving in said one direction to supply energy of asecond character first character to condition said secon-d signal to l0display its clear indication and to supply energy of the rst characterto said second line circuit, when supplied With energy of said secondcharacter to condition said second signal to display its cautionindication and to supply energy of said 15 second character to saidsecond line circuit, when supplied with energy of said third characterto condition said second signal to display its caution indication and tosupply energy of said third character to said second line circuit, andwhen not supplied with energy to condition said second signal to displayits stop indication and to supply energy of said third character to thesaid second line circuit, and electroresponsive means receiving energyover said second line circuit and controlling said third signal so as tocause said signal to display its clear, approach medium, caution or stopindications according as energy of the first, second or third charactersor no energy is supplied thereto.

HENRY S. YOUNG. RONALD A. McCANN.

